A hub bearing for use in a vehicle may include a seal device, which uses a ring-shaped seal to cover a space between an outer ring and an inner ring so as to inhibit the intrusion of foreign matters (such as water and dust) into the interior of the bearing and to prevent lubricant grease from leaking. In addition, since the hub bearing is required to allow a relative rotation between the inner ring and the outer ring, the outer circumference of the seal is fixed to the outer ring, and the inner circumference of the seal forms a sliding contact with the inner ring.
However, only with the seal covering the space between the outer ring and the inner ring, it is impossible to obtain a sufficient sealing performance for preventing water and dust from intruding into the bearing from the outside and preventing grease from leaking, and it is also hard to inhibit the grease leakage and to inhibit the intrusion of water and dust into the interior of the bearing from the space between the inner circumference of the seal and the inner ring.
Generally, in order to prevent foreign matters from intruding into the hub bearing, a seal retaining ring in the form of a shield plate is provided on an outer side of the seal in an axial direction. The seal retaining ring is fixed to the inner ring, and the inner circumference of the seal forms a contact with the seal retaining ring.
FIG. 1 shows a conventional hub bearing seal device as described above, wherein FIG. 1 is a cross-sectional view of a hub bearing according to the prior art, and FIG. 1A is an enlarged view of a portion 1A in FIG. 1. In FIG. 1, the hub bearing is a double row ball bearing, comprising: an outer ring 1′; an inner ring 3′; a retainer (not shown) for retaining double rows of balls (not indicated); a seal 2′ for covering a space defined between the inner ring 3′ and the outer ring 1′; and a seal retaining ring 4′ arranged on the outer side of the seal 2′ in an axial direction of the hub bearing. The inner ring 3′, the outer ring 1′, the seal 2′ and the seal retaining ring 4′ constitute the hub bearing seal device.
As shown in FIG. 1A, the outer circumference of the seal 2′ is fixed to the outer ring 1′ and is in a stationary state together with the outer ring 1′. The seal retaining ring 4′ is fixed to the inner ring 3′ and rotates together with the inner ring 3′. In FIG. 1A, the seal retaining ring 4′ is a ring-shaped metallic plate, which is bent into an L shape, one leg of which extends towards the interior of the hub bearing and is fixed to the inner ring 3′. In addition, the seal 2′ is provided therein with a metallic framework 23′, with which the outer circumference of the seal 2′ and the outer ring 1′ are fixed together. A first radial seal lip edge 22′ and a second axial seal lip edge 21′ are injection molded onto the metallic framework 23′ of the seal 2′, which two seal lip edges extend in the radial direction and the axial direction of the hub bearing and are brought into contact with the two legs of the L-shaped seal retaining ring 4′ in interference fit, respectively. Sealing is achieved by setting the degree of interference of the seal lip edges with the seal retaining ring, i.e., the amount of interference, wherein the first radial seal lip edge 22′ prevents the grease from leaking, and the second axial seal lip edge 21′ prevents external pollutants such as water and dust from intruding into the interior of the hub bearing.
In the hub bearing seal device of the prior art, the seal body forms the seal 2′ together with the metallic framework 23′.
A conventional hub bearing, which is provided with a seal 2′ as described above, for example, has a high starting torque, which is greatly higher than a running torque. As shown in FIGS. 2A-2B, the hub bearing with the seal has a running torque of 0.61 Nm, the hub bearing without the seal has a running torque of 0.29 Nm, the hub bearing with the seal has a starting torque of 1.35 Nm, and the hub bearing without the seal has a starting torque of 0.43 Nm. It can be obtained from the above that the starting torque generated by the seal is 0.92 Nm, which value is 2.14 times the starting torque of the hub bearing without the seal. The reason is when the bearing starts up, a high friction torque is generated due to the interference contact between the seal lip edges of the seal and the seal retaining ring.
In addition, since the lubrication is insufficient during the starting up stage, the friction torque generated by the seal accounts for a large proportion of the starting torque of the hub bearing. Further, since the starting torque is high and therefore it is not easy to start up, the conventional hub bearing requires a stronger drive device, which influences the performance of the hub bearing.
Thus there is a need for an improved hub bearing seal device.